Go up at roosting time and get them all situated before you turn out lights, know who is where, and then check on them first thing in the morning. You will know how is pooping what.
Liquid white thin poop can be caused from being chilled, not eating enough, stress, diet or illness. Coccidiosis can cause thin watery poop and sometimes, but not always, they pass blood as well. Cocci will cause them to stop eating and drinking. So while you are up at the coop at roosting time, check all crops to make sure everybody is eating. Run you hand down the right side of the breast and crops should be full at roosting time. If not, the bird is either ill or is being bullied away from food and water.
So whom ever is pooping this thin white poop, my make sure they are eating.